The present invention relates to a system for generating power. In particular, the invention relates to a system for generating power from two bodies of water.
There have been proposals to extract power from the movement of water using differential pressure and/or the influence of tidal effects. Examples of such proposals include hydroelectric dams, weirs and reservoirs.
One proposed system involves providing two walls to respectively dam a pair of inlets divided by an intervening promontory. Each wall extends from one side of its respective inlet to the promontory. A gate or lock is provided in one of the walls to regulate the level of water in that particular bounded inlet. Thus, in effect, two bounded reservoirs are formed, of which the water level of one can be adjusted by its gate or lock. A passage extending through the promontory allows fluid communication between the two reservoirs and a turbine is located within the passage. When there is a difference in water pressure between the two reservoirs electricity is generated by allowing water to flow through the passage and drive the turbine. The lock or gate is used to regulate the level of its bounded inlet to ensure it has a higher water level compared to the other bounded so as to create the difference in water pressure between the two reservoirs.
One disadvantage of the above system is that it requires the building of two separate walls, one with a lock or gate, to seal off the inlets. This results in significant expense and inconvenience in construction of the sealing walls and the gate or lock for the system. Another disadvantage is that the above system can only generate power by a one way movement of water from the designated high level water reservoir or inlet to the low level reservoir or inlet. Therefore, the system is dependent on recharging the high level reservoir, which can only be done when sea level is higher than the water level of the high level reservoir. In turn, the level of the designated high level reservoir must be higher than the designated low level reservoir, otherwise water would not flow from the high level reservoir to the low level reservoir.
The present Applicant believes that a possible solution or at the very least an economic alternative can be based on using natural tidal effects to generate power from localised areas of water with different water pressures.
The present invention provides a system for generating power, including:
a barrier partially dividing a body of water subject to tidal effects into two regions of water such that said regions of water have differing water levels over a tidal cycle;
a passage in said barrier for placing said regions of water in fluid communication with each other; and
means within said passage responsive to flow of water for driving a power generation means;
wherein water flows from one of said regions of water to the other of said regions of water via said passage when said regions have differing water levels during said tidal cycle.
The present invention is particularly applicable where there is a relatively large body of water, such as a bay, partially separated from a sea or ocean by naturally occurring land masses, such as those at the inlet of the bay. In this situation, water levels inside and outside the bay will take some time to equalise as the tide goes in or out. The invention takes advantage of the resulting difference in water levels inside and outside the mouth of the bay. Because tidal effects will cause one region of water to have a higher water pressure than the other region at certain times in a normal daily cycle (until this is naturally equalised through the unbounded body), there is no need to artificially create differences in water pressure between the two regions, as in the previously proposed system. The barrier need only be of sufficient size to induce differential water pressures in the two regions. The barrier may be completely natural in form or may include a man-made extension to an existing land mass. The barrier must be of a length sufficient to induce a time lag in water level equalisation as the tide rises or falls on one side thereof. A length in excess of 1 kilometer is preferable.
It is preferred that the barrier is a land mass, such as a peninsula, promontory, an isthmus or the like, which in combination with other naturally occurring land masses defines the two partially divided regions of water. Preferably, the power generation means may be driven by water flow in either direction. The regions of water may be localised zones in proximity to the ends of the passage.
The ends of the passage may have ports to facilitate the flow of water into the passage. The ports preferably have enlarged openings to facilitate the flow of water into the passage. The openings may be flared outwards, or may have a frusto-conical shape. In one embodiment the openings are curved funnels. Preferably, the ports each have filtering means, for example including a grating, for preventing objects entering the passage. The filtering means may also include a kink or s-bend in the passage to settle out water-borne solids from the water flowing through the passage. A sump may be provided at the kink or s-bend to remove the settled solids. The grating is preferably self-cleaning.
In one embodiment, the ports have one or more vertically extending conduits for further facilitating flow of water. The conduits preferably have mechanically closeable vents at one or more locations on the conduits for providing multiple entry points for water into and out of the passage. The vents may be automatically opened or closed in response to a sensed water level or on a tidal cycle.
Preferably, the means for driving the power generation means is a turbine driven by the water flow through the passage. The power generation means need not be located adjacent the turbine.
The present invention further provides a method for generating power, including the steps of:
providing a passage in a barrier, the barrier partially dividing a body of water subject to tidal effects into two regions of water such that said regions of water have differing water levels over a tidal cycle, the passage placing said regions of water in fluid communication with each other; and
driving a power generation means by driving means located within said passage in response to flow of water from said one of said regions of water to the other of said regions of water via said passage when said regions have differing water levels during said tidal cycle.
The passage preferably narrows near the means for driving the power generation means to increase the speed of flow of water at said means for driving the power generation means. Alternatively, the passage has a portion for increasing the speed of flow of water at said means for driving the power generation means. In this case it is preferred that the means for driving the power generation means is located near or at the end of the speed increasing portion. In a preferred embodiment, the speed increasing portion is substantially vertical.
A non-return valve is preferably provided in said passage downstream of said means for driving the power generation means to prevent the back flow of water in said passage.
In one preferred embodiment of the invention, the power generation means includes a first power generator;
said means for driving the power generation means includes a first means for driving the first power generator;
said passage includes a conduit in fluid communication with said regions of water and a first section in fluid communication with one region of said regions of water;
said first section being in fluid communication with said conduit via a first non-return valve and including said first means for driving the first power generator;
such that when said one region has a higher water pressure than the other region of said regions of water, water from said one region flows into said first section and said conduit, wherein water flowing through said first section drives said first means for driving the first power generator and enters into said conduit via said first non-return valve for discharge into said other region.
The above described arrangement provides for greater power generation efficiency over half of a tidal cycle.
Preferably, the first section has a portion to increase the speed of flow of water at said first means for driving the first power generator. It is preferred that the speed increasing portion of said first section is substantially vertical.
The system may include a plurality of first sections, each said first section including its own respective first power generator, first means for driving the first power generator and first non-return valve.
Preferably, the said conduit has one or more non-return valves to promote the flow of water from said one region to said other region.
The conduit may have an enlarged portion to promote the flow of water from said one region to said other region. Preferably, one non-return valve is located upstream from said enlarged portion. Preferably, a further non-return valve is located downstream from said enlarged portion.
In a modification of the previously described embodiment, the power generation means includes a second power generator;
said means for driving the power generation means includes a second means for driving the second power generator, and
said passage further includes a second section in fluid communication with said other region;
said second section being in fluid communication with said conduit via a second non-return valve and including said second means for driving the second power generator;
such that when said other region has a higher water pressure than said one region, water flows from said other region into said second section and said conduit, wherein water flowing through said second section drives said second means for driving the second power generator and enters into said conduit via said second non-return valve for discharge into said one region.
This modified embodiment allows for greater power generation efficiency where there is a reversible flow of water through the system caused by differential water pressures in both regions of water over a tidal cycle.
The second section preferably has a portion to increase the speed of flow of water at said second means for driving the second power generator. The speed increasing portion of the second section may be substantially vertical.
The system preferably includes a plurality of second sections, each said second section including its own respective second power generator, second means for driving the second power generator and second non-return valve.
The conduit may have an enlarged portion to promote the flow of water between said regions of water. The conduit preferably has one or more two-way valves to promote the flow of water between said regions of water. A two-way valve may be provided at one end or both ends of the enlarged portion.